Inappropriate Sinus Tachycardia

Causes of inappropriate sinus tachycardia 

The exact cause of IST is not always clear, but it may be linked to: 

• Abnormalities in the heart's electrical system that result in an overactive sinus node (the heart's natural pacemaker). 
• Autonomic nervous system dysfunction, where the body’s regulation of heart rate becomes impaired. 
• Hormonal changes, like those seen in hyperthyroidism. 
• Chronic stress or anxiety, which can trigger or worsen symptoms. 
• Certain medications, like stimulants or drugs that affect the sympathetic nervous system. 

Risk factors for inappropriate sinus tachycardia 

Several factors may increase the likelihood of developing IST, including: 

• Being female. IST is more common in women, especially young adults. 
• A history of anxiety or stress-related conditions.
• Thyroid problems, particularly hyperthyroidism. 
• A family history of heart arrhythmias or other conduction disorders. 
• Use of certain stimulants, medications or drugs that can increase heart rate. 

Symptoms of inappropriate sinus tachycardia 

The symptoms of IST can vary but typically include: 

• A consistently fast heart rate (over 100 beats per minute), even when resting. 
• Heart palpitations or the sensation of a racing heart. 
• Dizziness or lightheadedness, especially when being physically active. 
• Shortness of breath or fatigue. 
• Chest discomfort or tightness in some cases. 

Diagnosing inappropriate sinus tachycardia 

Diagnosing IST involves: 

• Electrocardiogram (ECG or EKG) to check for an elevated heart rate and to rule out other arrhythmias. 
• Using a holter monitor, which records the heart’s electrical activity over a 24-hour period to capture episodes of tachycardia. 
• Blood tests or blood panels to rule out thyroid issues, electrolyte imbalances, or other underlying conditions. 
• Autonomic function testing, sometimes used to assess the sympathetic and parasympathetic nervous systems. 

Treatment of inappropriate sinus tachycardia 

Treatment for IST often focuses on managing symptoms and may include: 

• Beta-blockers or calcium channel blockers to slow the heart rate. 
• Medications to address underlying issues, such as thyroid hormones if hyperthyroidism is present. 
• Lifestyle changes, including stress reduction techniques or avoiding stimulants like caffeine. 
• In severe cases, catheter ablation may be considered to modify the sinus node activity.